This invention relates to AC to DC conversion. Power distribution from electrical utilities is provided in the form of three phase AC so that there is a continuous flow through the lines. In the world it has been recognized that it would be desirable to reduce the amount of energy required to provide electrical energy for our equipment. One of the goals to achieve this is to improve the power supply efficiency, and to achieve a power factor of one.
My invention arose from a need in a plan that would impose upon users the requirement that power supplies for computers achieve a high power efficiency and yet have low harmonic distortion on the utility line. High harmonic distortion is generally caused by many separate units drawing current not fully tracking the input harmonic, and this is a problem which is often caused by computers and will need to be overcome by some means or the other. How this can be efficiently achieved is a problem solved by the present invention.
As general background it is recognized that there are many patents in the art related to three phase AC to DC converters and there are also many inverters. General background patents include U.S. Pat. Nos. 4,805,082; 4,533,987; 4,672,520; 5,331,994; 4,567,555; 4,504,895; 4,833,584; 4,084,220; 4,638,418, 4,866,592; 4,502,106; 4,675,802; 4,761,725; and 4,885,675.
However, faced with the need to draw high power with low harmonic distortion on the line, typically in the past a costly technique would be chosen by those skilled in the art. These costly techniques historically have included the use of motor generator sets which run off the utility's line and provide the isolated DC voltage with a step up or step down from the utility's voltage. Others might employ a rectifier (AC to DC) feeding an inverter with a regulated output.
A three phase rectifier feeding an inverter which provides a stepped up or down voltage as an output could be used. Some such rectifiers could feed a capacitor, and have the capacitor connected to a regulated inverter.
There is a need for three phase AC to DC converters with sinusoidal input currents, which may be made with low weights and with a shod design cycle as required for a power supply design and which will have high reliability and high power density, and the above mentioned approach is not suitable.
U.S. Pat. No. 3,737,755 issued Jun. 5, 1985 describes a DC to DC converter with a DC driven regulated current source driving an unregulated converter. I have recognized that such a converter could be useful, but as described it fails to even suggest any applicability to the problem to be solved. In the related application I have described such a converter in more detail and then disclosed my invention for a DC to DC converter which saves energy by recirculation. There would be a similar need in AC applications.
Also in the prior art are publications. The IEEE Transactions on Industry Applications, Vol. 1A-12, No. 4, July/August 1976 contains the article by E. T. Calkin et al, entitled "A Conceptually New Approach for Regulated DC to DC Converters Employing Transistor Switches and Pulsewidth Control", pages 369-377. Our invention could be used with this topology, see page 375.
Recovery of energy in switching regulators is discussed in other applications, see IEEE Transactions on Power Electronics, Vol. 3, No. 1, January 1988, pp. 26-30. However, the use of some sod of energy recovery for current fed inverters is not suggested. What is now recognized as a need to be solved is the ability to provide a power source which draws a current with a very low harmonic content from a utility and which will be able to have a power factor of one, without risk of blow ups, hazards caused by electromagnetic fields, and additional expense which may be caused by other possible circuits which may achieve a similar result.